ORTHO pt 1 Flashcards
nearly ___% of adolescents and adults have severely crowded incisors
- 15%
- this suggests that extraction of teeth would be necessary to create enough space to align them
an overjet of greater than ___mm suggests a class II malocclusion. what percent of children, adolescents, and adults have a class II malocclusion?
- 5mm
- children 23%
- adolescents 15%
- adults 13%
a reverse overjet suggests which malocclusion classification?
- class III
- less frequent than class II in the US
class II malocclusion is more common in what population? what bout class III malocclusion?
- class II whites of northern european descent
- class III asian populations (2-5%)
which percentage of the US population falls into each of angle’s four major classification groups?
- class I normal occlusion: 30%
- class I malocclusion: 50-55%
- class II malocclusion: 15%
- class III malocclusion: 1%
which theory of growth control states that bone, as all other tissues, is directly under the control of genetics
direct genetic control
which theory of growth control states that cartilage is the primary determinant of skeletal growth and indirectly controls the growth of bone; cartilage grows and is then replaced by bone
epigenetic growth control
which theory of growth control states that growth of bone is influenced by adjacent soft tissues through environmental changes in forces exerted on the bones that stimulate their growth
environmental growth control (functional matrix theory)
which type of bone formation is described as the formation first of cartilage, then transformation into bone?
- endochondral bone formation
- bones formed in this way are probably less susceptible to environmental influences during growth and are under more direct genetic control
how are bones of the cranial base formed?
endochondral bone formation
which type of bone formation is described as formation by secreted bone matrix directly within connective tissues, without intermediate formation of cartilage?
- intramembranous bone formation
- growth of intramembranous bones is more influenced by the environmental forces around them
how are bones of the cranial vault, maxilla, and mandible formed?
intramembranous bone formation
at birth, bones of the cranial vault are widely separated by ___ at the fontanelles. ___ of bone along the edges of the fontanelles eliminates these open spaces, but the bones remain separated by the ___.
- loose connective tissues
- apposition
- cranial sutures
as brain growth occurs, bones of the cranial vault are pushed apart, and ___ of new bone occurs at the sutures. describe remodeling.
- apposition
- remodeling also occurs with new bone added on the external surfaces and removed on the internal surfaces (periosteal apposition and endosteal resorption)
which bones make up the cranial base?
- ethmoid, sphenoid, and occipital bones
- formed initially in cartilage and later transformed into bone by endochondral ossification
as ossification of the cranial base occurs, three bands of cartilage remain, which are important growth centers called ___. what are the names of them?
- synchondroses
- sphenoethmoid synchondrosis
- intersphenoid synchondrosis
- sphenooccipital synchondrosis
each synchondrosis of the cranial bases acts like a two-sided epiphyseal plate with growing cartilage in the middle and bands of maturing cartilage cells extending in both directions that are eventually replaced by bone. these synchondroses eventually become inactive. describe when this occurs.
- intersphenoid around age 4
- sphenoethmoid around age 7
- sphenooccipital considerably later
why are bones of the cranial base minimally affected directly by growth of the brain?
because they are endochondral bones
what type of bone growth occurs in the maxilla?
intramembranous
where does bone growth of the maxilla occur?
at the sutures posterior and superior to the maxilla at its connections to the cranium and cranial base, and by surface remodeling
what direction does the maxilla grow?
- it migrates downward and forward away from the cranial base and undergoes significant surface remodeling
- surface remodeling includes resorption of bone anteriorly and apposition of bone inferiorly
during growth of the maxilla, much of the anterior movement is negated by ___, and downward migration is augmented by ___
- anterior resorption
- inferior apposition of bone
increased space for the eruption of maxillary posterior teeth occurs by ___
addition of bone posteriorly at the tuberosity as the maxilla migrates downward and forward
how does growth of the mandible occur?
both endochondral and intramembranous
describe bone growth of the mandible
- endochondral ossification at the condyles (develops independently and later fuses with ramus)
- intramembranous ossification in all other areas
during embryonic development, the mandible develops in the same area as the cartilage of which pharyngeal arch? what is the name of the cartilage?
- first pharyngeal arch
- meckel’s cartilage
- development of the mandible itself proceeds just lateral to meckel’s cartilage and is entirely intramembranous in nature
when meckel’s cartilage disintegrates during embryonic development, what happens to its remnants?
- they are transformed into a portion of two of the small bones of the middle ear (malleus and incus)
- its perichondrium persists as the sphenomandibular ligament
T or F:
during formation of the maxilla and mandible, interstitial growth occurs within the mineralized mass
false, this is impossible
space for eruption of the posterior mandibular teeth occurs as ___
- the anterior portion of the ramus resorbs extensively
- extensive surface apposition occurs on the posterior surface of the ramus
what is average closing rotation?
- in most children, condylar growth exceed molar eruption, and the mandible rotates slightly closed over time
- the closing rotation, along with the downward and forward growth of the mandible itself, helps make the chin appear more prominent as children age
- it also indicates that posterior face height increases more than anterior face height in most cases
what is severe closing rotation?
in some children, condylar growth greatly exceeds molar eruption, and the mandible rotates more substantially closed, leading to development of a shorter face and a deeper anterior overbite tendency
what is opening rotation?
- rarely, condylar growth is less than molar eruption, and the mandible rotates open during growth
- in these children, a long lower face and tendency for an anterior open bite develop
in general, structures ___ from the brain grow more and later
- farther
- for example, the mandible is farther from the brain than the maxilla and grows more and later
in the third month of fetal development, the head takes up almost ___% of the total body length. by the time of birth, the trunk and limbs have grown so that the head is ___% of the body. in an adults, the head represents about ___% of total height.
- 50%
- 30%
- 12%
neural tissues, including the brain, continue to grow rapidly after birth and reach near 100% adult size by what age?
6-7
lymphoid tissues, including tonsils and adenoids, grow quickly, reaching twice the adult size by about age ___, and then involute during the ___ growth spurt to reach adult size
10, pubertal
___ tissues do not grow much until puberty and then rapidly increase to adult size corresponding to the time of the pubertal growth spurt
genital or reproductive tissues
describe the growth rate of general body tissues, including muscle and bone
grow rapidly after birth, then slow in growth during childhood, and then accelerate again at the same time as reproductive tissues proliferate
the maxilla, located closer to the brain than the mandible, grows earlier and follows a pattern closer to that of ___ tissues
neural
the mandible grows later than the maxilla and exhibits more characteristics of a growth spurt paralleling the ___
pubertal growth spurt in body height
what does the growth velocity curve show?
- that growth height is very rapid after birth but decelerates quickly to a lower, more constant level in childhood
- around puberty, growth accelerates again, reaching a pubertal growth peak before slowing and virtually stopping at maturity
why is predicting the timing of growth spurts important for orthodontic treatment?
designed to take maximal advantage of growth changes
describe growth peaks of boys versus girls
- girls reach their growth peak about 2 years earlier on average than boys
- average peak growth for girls is around age 12 and for boys is around age 14
generally, the earlier the peak of growth, the ___ the duration of the growth spurt will be, and ___ overall growth occurs
- shorter
- less
- girls generally start growth sooner, grow for a shorter amount of time, and grow less than boys
what are the predictors of growth, and how reliable are they?
- chronologic age (not a great predictor)
- dental age (even less predictable)
- skeletal age (good correlation; determined by the relative level of maturation of the skeletal system)
- sexual development and growth in height are well correlated
what is the standard for assessing skeletal development?
- a hand-wrist radiograph, which reveals the ossification of the bones of the hand and wrist
- another possibility is evaluating the development of the vertebral bones as visualized on a ceph
- plot increases in body height over time
- compare successive ceph radiographs
describe directions of growth of the jaws over time
- growth in width is generally completed before the adolescent growth spurt begins
- growth in length continues through the growth spurt
- vertical growth continues longer
what is the most common craniofacial defect?
- cleft lip, palate, or both
- second only to clubfoot in congenital deformities
- occurs in 1/700 births
nearly all the tissues from the face and neck originate from the ___
ectoderm
cleft lip occurs when there is a failure of fusion of which two processes?
- frontonasal (medial nasal) process and the maxillary process
- this fusion includes the lip and alveolar ridge (the primary palate)
- closure of the secondary palate occurs about 2 weeks later, when the palatal shelves elevate and join together in a process that proceeds from anterior to posterior
what are the stages of normal dental development?
- gum pad stage
- primary dentition stage
- mixed dentition stage
- permanent dentition stage
the gum pad stage occurs at what age? when does it end?
- birth to about 6-7 months of age, ending with the eruption of the first incisor
- the future position of the teeth can be observed by the elevations and grooves present on the alveolar ridges
the primary dentition stage starts with the eruption of the primary teeth and lasts until about age ___, when the first permanent tooth erupts
6
maxillary anterior primary teeth are about ___% the size of their permanent successors
75%
the mandibular anterior primary teeth are about ___mm narrower mesiodistally on average than their successors
6mm
___, defined as the vertical overlap of the mandibular teeth by the maxillary teeth, develops as teeth erupt
overbite
how is overbite measured? what is the average overbite?
- can be measured in mm, but is preferable to measure in percentages
- 10-40% is normal
___ is the lack of overbite
open bite
open bite or reduced amount of overbite is not unusual in children during the primary dentition because of ___
thumb or finger sucking habits
___ is the horizontal distance between the mandibular teeth and the maxillary teeth
overjet
what is the normal range of overjet? what habits can increase overjet?
- 0-4mm
- digit sucking habits can increase overjet
children in the primary dentition often have generalized spacing between their teeth. the extra space helps accommodate ___
- accommodate the larger sized permanent teeth as they erupt
- if a child lacks spacing or has crowding in the primary dentition, the permanent dentition will exhibit crowding
spacing in the primary dentition is especially noticeable in what locations? what is this space called?
- located between the lateral incisors and canine in the maxilla, and between the canine and first primary molar in the mandible
- called the primate space
is crowding common in the primary dentition?
no
describe the following molar relationships in primary dentition: flush terminal plane, mesial step, distal step
- flush terminal plane - the distal aspects of the second deciduous maxillary and mandibular molars are at the same sagittal level
- mesial step - the mandibular terminal plane is mesial to the maxillary terminal plane
- distal step - the mandibular terminal plane is distal to the maxillary terminal plane
by the age of 5, about ___% of children have a terminal plane relationship that is flush or with a 1-mm or greater mesial step
90%
the ___ relationship of primary teeth determines the molar classification in the mixed dentiton
- terminal plane relationship
- the first permanent molar is guided along the terminal plane during eruption
in the mixed dentition stage, as each permanent tooth erupts, it is expected that its antimere (corresponding contralateral tooth) will erupt within ___ months
6
what is the “ugly duckling stage”?
- as the maxillary central incisors erupt, they move labially, and a temporary diastema is often present between them
- normal stage of development but does not always occur
- when permanent canines erupt, their mesial movement will likely close the diastema if one is present and if it is 2mm or less
in the mixed dentition phase, a transient open bite may be observed as a result of ___
- partial eruption of anterior teeth
- under normal conditions, the open bite resolves with further tooth eruption
the angle classification is based on the anterior-posterior relationship of which teeth?
the first mandibular molar to the maxillary permanent first molar
class I molar relationship is also called ___
normo-occlusion
class II molar relationship is also called ___
disto-occlusion
class III molar relationship is also called ___
mesio-occlusion
in predicting molar relationships, during the transition period from the primary to the mixed dentition, flush terminal plane develops into a class I in ___% of cases and into a class II in ___% of cases. mesial step can translate into which molar classifications?
- 56%
- 44%
- class I or class III (much less common)
what are the normal characteristics of the mixed dentition?
- molar and canine relationships are class I
- leeway space is present
- well-aligned incisors or up to moderate crowding of the incisors
- proximal contacts are tight
what is leeway space?
- the difference in mesiodistal size between the primary canine, primary first molar, and primary second molar and their permanent replacements
- leeway space is larger in the mandibular arch, averaging 2.5mm per side
- maxillary arch leeway space measures about 1.5mm per side
the leeway space can affect the eventual ___ of the molar in the permanent dentition or may aid in resolution of ___, or both
- classification
- crowding
in the permanent dentition, the maxillary teeth should overlap the mandibular teeth in which two directions?
vertically and buccolingually
what is the curve of spee and curve of wilson?
- arch curvatures
- curvature in the sagittal plane is the curve of spee
- curvature in the frontal plane is the curve of wilson
overbite in the permanent dentition is generally ___% but can vary up to ___%. overjet should be ___mm
- 10-20%
- 50%
- 1-3mm
the interarch relationship of the permanent dentition (also called ___) should be class I molar, premolar, and canine
buccal occlusion
permanent dentition relationships are fairly stable once established, with one notable exception. what is it?
during the second to fourth decades of life, there is a tendency for anterior crowding to develop or worsen over time
the maxillary intercanine width increases by approximately ___mm between the ages of 3 and 13. an additional increase of ___mm occurs until age 45.
- 6mm
- 1.7mm
the maxillary intermolar width in the primary dentition increases ___mm between the ages of 3 and 5. the permanent intermolar width increases by ___mm between the ages of 8 and 13, and decreases about ___mm by age 45
- 2mm
- 2.2mm
- 1mm
part of the increase in width of the maxillary arch is because ___
the alveolar bone is divergent, and the width increases as growth and eruption occurs
the mandibular intercanine width increases by ___mm from age 3 to 13. the intercanine width decreases by ___mm from age 13 to 45
- 3.7mm
- 1.2mm
the mandibular primary intermolar width increases by ___mm between the ages of 3 and 5. the permanent molar width increases by ___mm from age 8 to 13, and decreases by ___mm by age 45
- 1.5mm
- 1mm
- 1mm
how is arch length is measured?
at the midline from a point midway between the central incisors to a tangent touching the distal surfaces of the second primary molars or the mesial surfaces of the first permanent molars
in the maxilla, there is a small decrease in arch length with age because ___
the incisors become more upright
in the mandibular arch, a decrease in arch length with age is observed in both the mixed and permanent dentition as a result of ___
uprighting of the incisors and the loss of the leeway space
___ is a measure of the amount of space available for the dentition
circumference (perimeter)
how is circumference (perimeter) measured?
-measured from the distal aspect of the second primary molar (mesial aspect of the first permanent molar) on one side and around the arch to the distal aspect of the second primary molar on the other side
mandibular arch circumference decreases significantly in the mixed to permanent dentition because of what?
- mesial shift of the permanent molars into the leeway space
- the mesial drift tendency of the posterior teeth in general
- the slight amount of interproximal wear
- lingual positioning of the incisors secondary to the differential growth of the maxilla (less) compared with the mandible (more)
with age, does maxillary arch circumference increase or decrease?
increases very slightly
eruption is earlier by ___ months on average in females compared with males
5
primary teeth begin calcification between the ___ and ___ month in utero
3rd and 4th
T or F:
in the development of the primary dentition, the mandibular teeth usually start the calcification process before the maxillary teeth
true
eruption of the first primary tooth starts at about ___ months of age, and new teeth continue to erupt until age ___
- 6-7 months
- 2-3 years
what is the typical sequence of eruption of primary teeth?
central incisor, lateral incisor, first primary molar, canine, second primary molar
when do the permanent teeth begin calcification?
shortly after birth
when does the first permanent molar shows signs of calcification? what about the 3rd permanent molar?
- second postnatal month
- 8-9 years
what is the mandibular arch eruption sequence?
first molar, central incisor, lateral incisor, canine, first premolar, second premolar, second molar, and third molar
what is the maxillary arch eruption sequence?
first molar, central incisor, lateral incisor, first premolar, second premolar, canine, second molar, and third molar
T or F:
in the mandibular arch, the eruption sequence in the posterior segments is frequently asymmetrical
false
maxillary arch
what are a couple medical problems that may affect orthodontic treatment?
- susceptibility to periodontal disease
- medications that inhibit bone remodeling (bisphosphonates)
what aspects of social and behavioral assessment are important when considering orthodontic treatment?
cooperation and habits
what are class II division 1 and division 2 classifications?
- division 1 maxillary incisors are flared
- division 2 maxillary incisors are upright (laterals are flared) and deep overbite
in normal arch width, the maxillary lingual cusps will articulate with the ___
mandibular fossa
in crossbite or lingual crossbite, the maxillary ___ cusp is in the mandibular fossa
buccal
what is complete lingual crossbite?
- the whole maxillary tooth is lingual to the mandibular tooth
- in complete buccal crossbite, the whole maxillary tooth is buccal to the mandibular tooth
when examining facial esthetics and proportions, how is lip posture (lip competence) assessed?
- with the teeth together and the lips at rest, the lips should slightly touch or be slightly apart
- a gap of more than 3-4mm indicates lip incompetence because of a long lower face, protruding incisors, large overjet, or short lips
incisor show at rest (lip to tooth) is the amount of upper incisor below the upper lip. ___mm is considered esthetically pleasing
2-4mm
how many mm of gingival show on smile is considered esthetically pleasing?
1-2mm (more is excessive)
what are the facial convexity classifications?
- convex (more convex than average, class II)
- straight (average, class I)
- concave (prognathic, midface deficient, class III)
how is lip prominence evaluated?
- relative to rickett’s esthetic line, which extends fromt he tip of the nose to the chin
- lips should be slightly behind this line for esthetics
- incisor anterior-posterior affects lip prominence
what are the lip prominence classifications?
- full (procumbent, protrusive)
- average
- flat (retrusive)
what is the nasolabial angle?
angle between the base of the nose and the upper lips; should be perpendicular or slightly obtuse
what are the classifications for nasolabial angles?
- acute (usually along with full lips)
- average
- obtuse (usually along with flat lips)
what are the cephalometric reference planes (lines)?
- S-N: anterior cranial base
- FH: frankfort horizontal (Po-Or)
- OP: occlusal plane
- MP: mandibular plane (Go-Me or Go-Gn)
what is the SNA?
anterior-posterior position of the maxilla (bigger means maxilla is more anterior)
what is the SNB?
anterior-posterior position of the mandible (bigger means mandible is more anterior)
what is the ANB?
anterior-posterior difference between maxilla and mandible (more positive indicates skeletal class II; more negative indicates skeletal class III)
what is the MP-SN?
mandibular plane angle (bigger is steeper and indicates vertical growth pattern, with long lower face and anterior open bite tendency)
what is the Y-axis S-N to S-Gn?
bigger indicates more vertical development, with long lower face and anterior open bite tendency
what is 1/-SN?
upper incisor angulation (bigger is more flared)
what is /1-MP?
lower incisor angulation (bigger is more flared)
T or F:
individual cephalometric measures can be used themselves to make a diagnosis
false
T or F:
cephalometric measures can in themselves be considered problems
false
however, they can indicate what may be a problem (protrusive maxilla, small mandible, flared maxillary incisors, vertical growth tendency)
in prioritizing a patient’s problem list, what usually take top priority?
systemic diseases or pathology
within occlusal problems, do interarch or intraarch relationships take priority?
- interarch
- however, priority may vary depending on severity
ideal goal of treatment is to achieve the best possible function, esthetics, and stability for each patient. can these typically be achieved by a reasonable orthodontic plan?
- not often
- one goal may need to be sacrificed at the expense of achieving the best possible result for a given patient
in tooth movement, the amount of force (heavy or light) determines the biologic pathway of tooth movement and the formation or lack of formation of ___
a hyalinized zone with undermining resorption
describe remodeling of the PDL during orthodontic tooth movement
- under physiologic conditions, the PDL is rich in collagen fibers well organized to resist the forces of mastication
- remodels significantly during orthodontic tooth movement
what is the pressure or compression side of a moving tooth?
- side toward which the tooth is moving
- bone resorption takes place on this side (result of osteoclastic activity)
- resorption lacunae created are called howship’s lacunae
what is the tension side of a moving tooth?
- side opposite to the direction of the movement of the tooth
- apposition of bone occurs on this side
when a tooth is intruded, the area of compression of the PDL is concentrated at which part of the tooth?
apex
which type of tooth movement creates two areas of compression?
tipping (crown and apex move in opposite directions)
during bodily movement of a tooth (translation), the side of the PDL toward which the tooth is moving experiences ___, and the other side experiences ___
compression, tension
during tooth movement, tension and compression occur in the PDL and its two interfaces. what are they?
with the bone on the alveolar side and with the cementum on the dental (tooth) side
forces ranging from ___ are experienced by the PDL during mastication, and the supporting apparatus of the tooth (alveolar bone and PDL) undergoes bone bending and compression and tension of the PDL
1-50kg (or 10-500N)
describe the use of heavy orthodontic forces in relation to tooth movement efficiency
- heavy orthodontic force does not make tooth movement more efficient
- it actually delays tooth movement by causing a lag period after the initial movement of the tooth within the PDL
describe the initial period of tooth movement due to heavy forces
- bone bending and the creating of piezoelectric signal occurs in less than 1 second
- the PDL is compressed, and fluid is expressed from the area of compression, resulting in instant movement of the tooth within the PDL in 1-2 seconds
- as the fluids are expressed from the PDL, pain is felt as a result of pressure applied within 5 seconds
- undermining resorption occurs within the alveolar bone (in the marrow spaces) and moves toward the PDL area
during the initial period of tooth movement from heavy forces, appearance of ___ in the bone marrow spaces is the first indication of undermining resorption
osteoclastic cells
during the initial period of tooth movement from heavy forces, undermining resorption can last how long?
- 2 to a few weeks
- no tooth movement can occur until the undermining resorptive process is completed when heavy orthodontic forces are applied
in tooth movement from heavy forces, during undermining resorption, the compressed PDL undergoes significant tissue changes. describe these changes
- on the compression side, the hyalinized zone starts to develop (an area of the PDL that has lost all structural organization shows signs of necrosis and a lack of cellular activity)
- hyalinization of the PDL occurs within hours of the application of a heavy force
during initial tooth movement form heavy forces, after hyalinization of the PDL, cells from the surrounding bone marrow start to migrate into the area from the bone marrow spaces within ___ days, and ___ simultaneously starts within the bone marrow spaces
- 3-5 days
- undermining resorption
describe the secondary period of tooth movement from heavy forces (after undermining resorption)
- the hyalinized PDL is in the process of healing
- secondary tooth movement occurs after a lag period during which undermining resorption takes place
the use of light forces causes smooth, continuous tooth movement without formation of a significantly ___ in the surrounding PDL
- hyalinized zone
- as a result, teeth subjected to light orthodontic forces start to move earlier and in a more physiologic way than teeth subjected to heavy forces
during light tooth movement, initial reaction includes partial compression of the blood vessels and a distortion of the PDL fibers. within minutes, blood flow is altered, the ___ changes, and ___ and ___ are released within the PDL
- oxygen tension
- prostaglandins and cytokines
during light tooth movement, after blood flow is altered in the PDL, metabolic changes such as enzyme activity and chemical messengers that alter cellular activity start to appear in this area of the PDL after a few hours. what are the first messengers that have been suggested are included?
- hormones (parathyroid hormone and calcitonin)
- fibroblast distortion
- substance P
- some neurotransmitters
- prostaglandins
within a few hours after light force has been applied to a tooth, signal transduction starts in the PDL, and the second messenger (___) levels increase. cellular differentiation takes place in the PDL, and the coupling between ___ and ___ activities results in frontal resorption of the alveolus within a few days.
- cyclic adenosin monophosphate
- osteoclast and osteoblast
even when light forces are applied to a tooth, because the PDL itself is nonuniform and stresses created in the PDL vary depending on the location observed, it is likely that some areas along the tooth will experience some ___
undermining resorption
describe mobility of teeth subjected to orthodontic forces
- forces on the tooth cause the PDL to temporarily widen, resulting in moderate mobility of the teeth that resolves with completion of therapy as long as there is no active periodontal disease
- if the tooth is in traumatic occlusion or the patient is grinding or clenching, the mobility is significantly increased, and occlusion may need to be adjusted or at least monitored
pain that occurs as a result of heavy orthodontic forces occurs within a few hours of the initiation of the force, and lasts how long?
2-4 days
pain experienced after the application of heavy forces is due to the development of areas of ___
- ischemia or necrosis (hyalinization) in the PDL
- these areas undergo remodeling, and the pain decreases until the next appliance activation
what OTC pain medication should patients be given to alleviate pain resulting from orthodontic tooth movement and why?
- acetaminophen (tylenol) as opposed to aspirin or ibuprofen
- analgesic mechanism of acetaminophen does not completely overlap that of aspirin and ibuprofen
- may also have a more favorable adverse effect profile compare with aspirin and ibuprofen
during orthodontic tooth movement, tissue inflammation usually results from ___, but might be due to ___
- poor oral hygiene
- less likely cause is an allergic reaction to latex or nickel (20% of the US population has a nickel allergy)
during orthodontic tooth movement, is mild pulpitis common?
no; symptoms ranging from mild pulpitis to loss of vitality are rare
what teeth can loss of vitality occur in during orthodontic tooth movement?
- teeth that have a history of trauma or extensive restorations, or that are moved with unusually heavy force or over long distances
- if the apex of the tooth is moved out of the alveolar bone, the blood supply can be potentially severed, and the tooth may lose vitality
can teeth that have been successfully endodontically treated be moved orthodontically without concern?
yes, they do not appear to be more prone to root resorption than vital teeth
what are the genetic risk factors for root resorption during orthodontic tooth movement?
- family history of root resorption
- susceptibility to root resorption seems to be out of multifactorial polygenic inheritance
what are the force/movement factors that increase risk of root resorption?
heavier forces, certain types of tooth movement, and more movement of a tooth during treatment increase the potential for root resorption
which types of teeth are at higher risk of root resorption?
single-rooted teeth
teeth subjected to ___, ___, and ___ have a higher incidence of resorption
trauma, bruxism, and heavy masticatory forces
T or F:
a tooth that had signs of root resorption before initiation of treatment will likely continue to resorb during orthodontic therapy
true
which population is less at risk for root resorption?
asians are less at risk than hispanics or whites
teeth with substantial root resorption but intact ___ do not experience any more mobility than unresorbed teeth
marginal periodontium
what is the current standard of care for patients at risk for root resorption or presenting with root resorption at the onset of treatment?
- use light forces
- building periods of rest into treatment when wires are kept passive to allow for repair to occur
- taking periodic periapical radiographs to monitor the amount of resorption occurring
- detailed informed consent and good communication with the patient and parents and any referring providers
what is the rapid acceleratory phenomenon?
- it is possible to accelerate tooth movement by performing a surgical procedure involving tissue reflection and selective corticotomy cuts and perforations around teeth to be moved
- bone grafting is often performed
- followed by a period where tooth movement proceeds rapidly (rapid acceleratory phenomenon)
___ is movement of all points on the tooth in the same direction the same amount; there is no rotation
pure translation (aka bodily movement)
for a free body floating in space, the center of resistance is coincident with the ___
center of mass or gravity
for a tooth, the location of the center of resistance depends on what?
- the size and shape of the tooth
- quality and level of the supporting structures
in a healthy tooth, the center of resistance is presumed to be about 1/2 the distance from the ___ to the ___
- alveolar crest to the root apex
- this is about 10mm from where an orthodontic bracket would be located on the crown of a tooth
the center of resistance for a periodontally compromised tooth with loss of attachment is more ___
apical
a ___ is defined as a tendency to rotate and may refer to rotation, tipping, or torque in orthodontics
moment
describe the orders of tooth movement and rotation
- first order rotation (occlusal view)
- second order or tipping (buccal or lingual view)
- third order or torque (mesial or distal)
how is a moment created?
if a force is applied at any point other than the center of resistance (the center of resistance will also be moved in the direction of the force)
the ___ is the mathematical point about which the tooth appears to have rotated after movement is complete
center of rotation
increasing the magnitude of the force or applying the same force even farther from the center of resistance increases the tendency for ___
rotation
the magnitude of a moment (M) is equal to what?
the magnitude of the applied force (F) times the distance (d) of that force from the center of resistance (M=Fd)
a ___ is two equal and opposite, noncollinear forces
couple
a couple applied to a tooth produces ___ without ___
pure rotation without translation
when a couple has been applied to a tooth, the tooth rotates about its ___ regardless of the point of application of the couple
center of resistance
the magnitude of the moment created by a couple depends on what?
the force magnitude and distance between the forces (M=Fd)
how are couples applied in orthodontics?
by engaging a wire in an edgewise bracket slot
what are the 5 types of tooth movements?
- pure rotation
- tipping (uncontrolled tipping)
- crown movement (controlled tipping)
- pure translation (bodily movement)
- root movement
in pure rotation movements, the center of rotation is at the ___
- center of resistance
- when a couple is applied to a tooth, it rotates around its center of resistance
in tipping movements, the center of rotation is ___
- apical to the center of resistance
- crown and apex move in opposite directions
what is the easiest and fastest tooth movement to accomplish?
tipping (but is often the least desirable tooth movement)
how is crown movement (controlled tipping) accomplished?
- a force is applied at the bracket and a small couple is also applied to partially negate the tipping of the crown caused by the force
- slightly more difficult movement to produce and occurs more slowly
in crown movements (controlled tipping), the center of rotation is ___
at the root apex
how is pure translation (bodily movement) accomplished?
- a force is applied at the bracket; a larger couple is also applied to exactly negate the tipping of the crown caused by the force
- this is a difficult and slow type of tooth movement
in pure translation (bodily movement) movements, the center of rotation is ___
so far apical to the tooth (at infinity) that the tooth translates without tipping
how is root movement accomplished?
- a force is applied at the bracket, and an even larger couple is applied to more than negate the tipping of the crown caused by the force; only the root moves in the direction of the force
- most difficult and slowest type of tooth movement
in root movements, the center of rotation is ___
at the crown of the tooth
all orthodontic appliances obey which of Newton’s laws?
- third law
- for every action, there is an equal and opposite reaction
- it is impossible to design an appliance that defies this law of physics
for each orthodontic appliance, the sum of the forces and the sum of the moments acting on it sum to ___
zero
describe one-couple appliances
- inserted into a bracket at one end and tied as a point contact at the other end
- a couple is produced only at the engaged end
- equal and opposite forces (in a direction opposite to the couple at the engaged end) are produced at the two attachment sites
- the sum of the forces is zero, and the sum of the moments is zero
describe two-couple-appliances
- inserted into a bracket on both ends
- both a couple and a force are produced at each end
- the magnitude of the couple is largest at the end closer to the bend in the wire or at the bracket that is more severely angled in the case of a straight wire
- the sum of the forces is zero, and the sum of the moments is zero
___ is resistance to movement
anchorage
because forces applied to teeth are distributed along the root surface to activate cells in the PDL, the anchorage value of any tooth is roughly equivalent to its ___
root surface area
what is reciprocal tooth movement?
two equal anchorage value teeth or groups of teeth (units) are moved against each other and move the same amount toward or away from each other
what is reinforced anchorage?
- adding additional teeth to a unit to distribute the force over a greater area and slowing the movement of the anchor unit
- another method for reinforcing anchorage would be extraoral force, such as with headgear, with interarch elastics, or by using an implant
what is stationary anchorage?
-teeth meant to be the anchor are activated to undergo difficult, slow movements, such as bodily movement (translation) or root movement, which distribute forces dispersed over large areas of the PDL, whereas the reactive units undergo tipping, which occurs faster and more easily as a result of concentrated forces in the PDL
what is cortical anchorage?
- anchor teeth roots are moved into cortical bone, which resorbs more slowly that medullary bone
- this is a controversial concept because root resorption would likely be increased as roots are forced into cortical bone
describe the use of implants for anchorage
- implants, including palatal implants, miniscrews or temporary anchorage devices, and bone plates, can serve as absolute anchorage for holding or moving teeth
- a stable implant does not move because it has no PDL
